1. Field of the Invention
The present invention relates to detecting a position of a moving body and controlling travel.
2. Description of the Related Art
Conventionally known moving body systems include, for example, loaders for transferring articles such as workpieces or tools to and from equipment such as a machine tool, and overhead traveling vehicle systems for transferring articles such workpieces or reticles to and from equipment such as a semiconductor fabrication device. While providing a curved section on the trajectory of a moving body increases the flexibility with which equipment is disposed, feedback control of the travel cannot be carried out if the position of the moving body cannot be accurately measured in the curved section. Also, while it is convenient if the moving body can transfer articles to and from equipment in the curved section, this requires that the position of the moving body in the curved section be accurately measured, and that the moving body be stopped at a predetermined position.
In terms of the related art, JP 4513673B discloses a technique for detecting the position of a moving body in a curved section with linear sensors, and in particular, discloses a technique for shortening the effective range of linear sensors in a curved section. JP 4148194B discloses a technique in which, when a mark provided on the trajectory is read with an optical sensor and the distance that a moving body has traveled is derived, the traveled distance derived by the optical sensor is corrected using a ratio of the radius of curvature of the center of trajectory and the radius of curvature of the position where the mark is provided.
Incidentally, the curved section of the trajectory of a moving body may be other than a quarter circle or the like. When the curved section is configured as a quarter circle, the centrifugal force change suddenly at the entrance and exist of the curved section. In view of this, enlarging the radius of curvature at the entrance and exit of the curved section and reducing the radius of curvature in the middle portion of the curved section enables the change in centrifugal force at the entrance and exit of the curved section to be reduced. Also, although the moving body is guided by guide rollers or the like in the curved section, the moving body is guided less than perfectly at the entrance and exit of the curved section and tends to wobble. For the above reasons, it is difficult to accurately derive the position of a moving body in a curved section simply by correcting the ratio of the radii of curvature.